Electronic Telegram No. 738 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html COMET C/2006 M4 (SWAN) Z. Sekanina, Jet Propulsion Laboratory, California Institute of Technology, writes that a preliminary inspection of the astrometric observation of C. E. Woodward et al. from Nov. 7 of a detached-coma feature (cf. IAUC 8772), suggests that this is a compact cluster of sizable nucleus fragments, released from the primary at the time of a recent outburst (IAUC 8766). The cluster, rather than a single fragment, is implied by the feature's reported elongation along the offset vector, reminiscent of similar episodes experienced recently by comet 73P's nuclei B, G, and others. Assuming, tentatively, 2006 Oct. 23.9 UT for this event's onset time, the observed offset fits the modeled separation distance perfectly and leaves a residual of 3 degrees in the position angle, well within observational errors. The derived effective differential nongravitational deceleration, (69 +/- 4) x 10**-5 units of the sun's gravitational acceleration, implies that the cluster is a short-lived phenomenon, observable for a few weeks at the most. The cluster's predicted separation distances and position angles, relative to the primary nucleus (0h TT, equinox 2000.0), are: 2006 Nov. 11, 5", 39 deg; Nov. 21, 9", 35 deg; Dec. 1, 13", 31 deg; Dec. 11, 17", 27 degrees. Visual total-magnitude and coma-diameter estimates (cf. IAUC 8766): Oct. 25.72 UT, 4.2, -- (M. Meyer, Frauenstein, Germany, naked eye); 26.77, 4.2, 15' (M. Lehky, Pasinovice, Czech Republic, naked eye); 28.76, 4.5, 10' (V. Gonano, Udine, Italy, 10x50 binoculars); 30.75, 5.4, 20' (K. Hornoch, Vohancice, Czech Republic, naked eye); Nov. 1.73, 5.6, 10' (A. Diepvens, Balen, Belgium, 20x50 binoculars); 6.63, 5.8, 5' (V. Ivanov, Saratov, Russia, 0.11-m reflector); 8.79, 6.4, 6' (J. J. Gonzalez, Asturias, Spain, 7x50 binoculars); 11.86, 6.5, 9' (J. Carvajal, Madrid, Spain, 6x30 binoculars); 12.78, 6.3, 10' (Gonano). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2006 CBAT 2006 November 13 (CBET 738) Daniel W. E. Green